Certain shoes have a wedge or other type of insert in their heel portions. Often, a wedge insert is used to elevate the shoe's heel and to provide added strength or rigidity. Typically, the top surface of such an insert follows the contour of the upper surface of the shoe's sole, thereby providing support at every point along the wearer's foot.
Conventionally, such a shoe often is constructed by cutting out different layers that ultimately will make up the shoe's sole (i.e., the portion of the shoe that is beneath the wearer's foot) and then bonding those layers together using an adhesive material. However, prior to bonding two of such adjacent layers together, a wedge of the desired shape is inserted at the back of the shoe between such two adjacent layers. Then, instead of bonding the upper and lower layers directly together along their entire surface areas, the upper layer is bonded to the top surface of the wedge and the lower layer is bonded to the bottom surface of the wedge. For the portion of the shoe that is forward of the wedge, the two adjacent layers generally are bonded directly to each other.
Once all of the foregoing steps have been completed, the sides of the shoe's sole are ground down, in order to smooth out any sections where the layers do not match precisely, to de-emphasize any seams between the layers (e.g., to provide the appearance of a single non-layered material), and to provide any desired shaping of the sole's side surfaces (e.g., to provide rounding, grooves or other three-dimensional patterns).
Previously, the inventors listed in U.S. patent application Ser. No. 12/792,401 (the '401 application, now U.S. Pat. No. 8,914,992) discovered that, when using the conventional production technique described above, because a significant portion of the insert's side walls also are exposed, the grinding of the layers comprising the shoe's sole almost necessarily results in grinding at least a portion of the inserted wedge. That is, even manual grinding usually could not be limited strictly to the other layers of the shoe's sole; some of the grinding would overlap onto the sides of the insert. Any attempts to prevent such overlap generally would require extreme care that would substantially increase the cost of the finished product and, therefore, would be unfeasible for mass, medium-scale or large-scale production. The end result would be that at least some portion of the inserted wedge (e.g., along its bottom and top edges) also would be ground down.
For some shoes, this result was acceptable or even desirable. The best example of such a case was where there was a desire for the shoe's heel to have a uniform appearance, i.e., so that there is no indication that the heel is in fact comprised of multiple layers and a separate wedge. Depending upon the type of grinding surface that is used, the side walls of the shoe's heel would appear to be uniformly smooth or textured.
However, the '401 application observed that such a manufacturing technique limits the types of wedges and other inserts that can be used within a shoe's sole, as well as the variety of shoe designs that can be made with an insert. For example, using such a conventional technique generally precludes one from inserting a decorative wedge, or at least one that has a fully decorated outer surface, because the subsequent grinding generally would obliterate such surface decorations. At the same time, simply omitting the grinding step generally would have the undesirable effect of leaving intact any production imperfections that exist after the individual layers have been bonded together.
The '401 application addressed this problem by providing a production technique in which a temporary insert is placed into the heel of a shoe (e.g., to provide the shoe with its desired final shape) during the grinding process. Then, upon completion of the grinding process, the temporary insert is removed and replaced with the desired permanent insert.
Thus, in one aspect, the '401 application was directed to systems, methods and techniques for making a shoe sole, in which a shoe sole is preliminarily assembled by bonding together a plurality of layers with a temporary insert disposed between two adjacent layers. Then, an outer edge of the shoe sole is ground and, following that, the temporary insert is removed and a permanent insert is bonded in place of the temporary insert, such that the permanent insert forms a portion of a side wall of the shoe sole.
By virtue of the foregoing arrangement, it is possible, e.g., to produce a wide variety of shoes with decorative inserts, which would not be possible, or at least would be significantly more difficult and expense to produce, using conventional techniques. However, it remains very desirable to have additional improvements, particularly with regard to the use of insert pieces within the heel portions of shoes.